A typical example of a formed metal panel is an aircraft wing panel. Such panels have longitudinal ribs on their undersides for strengthening and/or stiffening the panel. These ribs complicate the metal-forming process when the panel is shaped into its desired configuration. It is often desired to form a wing panel with a dihedral configuration, and also, often in addition, give the panel a curved form in a direction normal to the dihedral to form a “saddleback” configuration.
Hitherto, wing panels have been formed with a dihedral, by shot peening. However, the strengthening/stiffening ribs are discontinued in the vicinity of the bend, or bends, to permit the panel to be formed. This limits the strength of the panel and the final wing, and often extra material has to be provided to maintain a desired consistent strength for the whole panel and the associated wing structure.
Considerable prior art describes metal forming by shot peening. One example, for forming an aircraft wing skin panel, is U.S. Pat. No. 4,329,862, Harbum et al, which describes shot peening flat sheets on both sides in predetermined patterns to create localized growth and to match a span wise curve, and on one side to match a chord-wise curve. U.S. Pat. No. 4,694,672, Baughman, describes shot peening of an aircraft skin in narrow bands or strips span-wise on a common chord to form a simple curve. U.S. Pat. No. 3,705,511, Brandel et al, deforms by metal balls falling under gravity. U.S. Pat. No. 4,350,035 describes shaping or forming an article by shot peening or blasting.
None of the prior art describes the forming of metal panels having integral ribs which are continuous over the locality or localities at which the panel is formed. Prior art techniques require that the ribs be discontinuous in the region of a bend to avoid compression or tension on the ribs. In order to provide a curved ribbed panel having superior characteristics, it is desirable to provide a method for forming a completely curved panel with a continuous rib structure.